Could chemical weapons in Syria force Obama's hand?

President Obama last August declared that any use or transport of Syria's chemical weapons would constitute a 'red line' for US policy toward the country. Now Israel, Britain, and France say they have evidence that Syria has crossed that line.

A man with a chemical mask on his head searches for survivors from the rubble of a damaged area, which activists said was a result of an airstrike by the Syrian regime, in the Al Sukkari neighborhood in Aleppo, Syria, in early April.

Washington — President Obama may soon have to come to grips with what it means to issue a "red line" to a foreign government.

On Tuesday, Israeli military officials said they have evidence and are "nearly 100 percent certain" that forces of Syria's Bashar al-Assad regime have used chemical weapons – a step Mr. Obama said would be a game changer for the United States in its policies toward Syria and the civil war raging there. Last August, Obama declared that any use or even "moving around" of Syria's substantial chemical weapons stockpile would constitute a "red line" for the US – any crossing of which "would change my calculus … change my equation."

With the closest US ally in the region now asserting that chemical weapons have been used, Obama will come under more pressure to demonstrate – possibly through the use of American force – that his "red line" was not a hollow threat, US foreign-policy analysts say.

"If you make a flat statement like that and you don't follow it up, then you undermine your credibility," says Lawrence Korb, a former Pentagon official who is now a national security analyst at the Center for American Progress (CAP) in Washington.

Obama has been reluctant to deepen US involvement in Syria's war, limiting US assistance to food and supplies for refugees and internally displaced Syrian civilians, and to nonlethal material for the rebel fighters the US supports. But use of chemical weapons by Mr. Assad's forces could prompt a more interventionist approach, some analysts say: for example, direct measures by US forces to destroy or safeguard Assad's chemical weapons. Obama could also cite a crossed red line as justification for arming the rebels or taking other, more robust measures to protect Syrian civilians.

Such measures might include establishing a no-fly zone over northern Syria, a step that already has bipartisan support in Congress, or creating "humanitarian corridors" for refugees to move along and for getting food and other supplies to the civilian population.

Probably a last resort, Mr. Korb says, would be "to send in special forces to grab the chemical weapons."

Pentagon officials said last month they were preparing a list of calibrated measures that the president could order in the event that chemical weapons are used. In response to the Israeli claims Tuesday, Pentagon spokesman George Little said the US "continues to assess reports of chemical weapons use in Syria."

Last week Britain and France sent a letter to United Nations Secretary-General Ban Ki-moon, in which they claim to have credible evidence that Syria had used chemical weapons more than once since December. The UN has assembled a team of experts that is awaiting permission from Assad to enter the country to investigate charges of chemical weapons use.

Calling any such use "entirely unacceptable," Mr. Little said, "We reiterate in the strongest possible terms the obligations of the Syrian regime to safeguard its chemical weapons stockpiles, and not to use or transfer such weapons to terrorist groups like Hezbollah."

The reference to Hezbollah, the radical Muslim organization in Lebanon known to be aiding Assad in his fight with the armed Syrian opposition, appeared to be a tip of the hat to Israel, which considers Assad's possible transfer of chemical weapons to enemies of Israel one of its greatest concerns.

Israel's assertion of chemical weapons use in Syria Tuesday came from Brig. Gen. Itai Brun, Israel's top military intelligence analyst. He said evidence from attacks on March 19 near Aleppo and Damascus, including photos of victims foaming at the mouth and exhibiting constricted pupils, suggested that a sarin-based nerve agent had been used.

Speaking at an international conference in Tel Aviv, Brun said it is disturbing that the chemical weapons use had not resulted in "any appropriate reaction" from the international community, "because it might signal that [such use] is legitimate."

US Defense Secretary Chuck Hagel, who is wrapping up a three-day visit to Israel Tuesday, has said the evidence of chemical weapons use so far is "inconclusive."

The US will continue trying to determine if chemical weapons were indeed used, and if so, what type and to what degree. But experts like CAP's Korb say that after the US drew a blanket "red line," any hedging over technicalities risks sounding like "an excuse" not to follow through.

"Generally when we think about the use of chemical weapons, we think about the cases of thousands of people dying," Korb says – such as in attacks on restive communities by Assad's father, Hafez al-Assad, in 1982, and by Iraq's Saddam Hussein in 1988.

"It doesn't appear from anything we know right now that this is what the Israelis and French and British are talking about," he adds.

Korb notes, however, that Obama never qualified his red line by saying, for example, that it would take "massive" use to cross it. "It's a reminder," he says, "that you have to be careful about what you say."